1. Field of the Invention
The present invention relates to portable computers, and more particularly to a portable computer having a telephone line input switching function and an expansion system for use with the portable computer.
2. Description of the Related Art
Recently, portable computers have become a popular alternative to traditional desktop computers in terms of their movability and simplicity. Further, various expansion devices have been developed for enabling the portable computers to extend battery life as well as perform multimedia functions. This is to overcome inherent functional limitations of the portable computer due to its reduced size and limited battery life. Those expansion devices, for example external speakers, external batteries or AC adapters and so forth are often incorporated into an apparatus, that is, a docking station fitted to a specific notebook computer.
Usually, the docking station is provided with a special port or connector called a "port replicator." In addition, various ports are provided so that peripheral devices such as a external display device, mouse or keyboard may be optionally connected to the docking station. The port replicator is coupled to an expansion port specially provided in the portable computer, to electrically and mechanically connect the portable computer to the docking station. With this connection, a total link can be made between the computer motherboard and the expansion devices as well as the peripheral devices of the docking station. Thus, enhancing the expandability of the portable computer is possible.
Further, the docking station may include a telephone line connector which facilitates the user to connect a telephone line to a modem board installed in the portable computer.
Such a telephone line extension system is connected to a portable computer having a modem board connected to the computer system including a CPU via a system bus. The modem board includes modem circuitry and a line interface section. Inputs of the line interface section are connected to a common telephone line via a modular jack called an RJ-11 female connector. This connector is preferably provided at a side wall of the computer main body. Telephone lines at the input of the modem are internally extended to terminals of an expansion port provided in the portable computer. Also, in the docking station, an extra telephone line connector is provided. The telephone lines leading from the connector are connected to terminals of a port replicator provided in the docking station. Thus, when the portable computer is docked with the docking station, and the port replicator is coupled to the expansion port, the telephone lines at the input of the modem can be extended to the extra telephone line connector of the docking station through the expansion port and port replicator. An RF-11 male connector at the telephone cable is coupled to the extra telephone line connector to establish a telephone line connection through the docking station. When the portable computer is used separately, another RJ-11 cable connector may be coupled to the connector of the portable computer.
However, such a telephone line expansion system has problems in that the telephone lines leading from the extra telephone line connector to the input stage of the modem board affects the electrical safety of the expansion port and the port replicator since the telephone lines are supplied with a high voltage and such a high voltage passes by relatively low voltage terminals of the expansion port and port replicator. Furthermore, high-voltage telephone lines provided in the docking station and the portable computer may cause considerable electromagnetic interference and electrostatic discharge.
The following patents each discloses features in common with the present invention but do not teach or suggest the specifically recited features of the present invention: U.S. Pat. No. 5,574,859 to Yeh, entitled Method And Apparatus For Using A Software Configurable Connector To Connect A Palmtop Computer Having A Custom Port To A Host Having A Standard Port, U.S. Pat. No. 5,265,238 to Canova Jr. et al., entitled Automatic Device Configuration For Dockable Portable Computers, U.S. Pat. No. 5,666,495 to Yeh, entitled Method And Structure For Data Transfer Between A Standard Port Of A Host Computer And A Custom Port Of A Palmtop Computer Using A Docking Station, U.S. Pat. No. 5,671,366 to Niwa et al., entitled Operating System Optimization To Permit Use Of A First Unit With A Second Unit To Extend The Functionality Of The First, U.S. Pat. No. 5,668,977 to Swanstrom et al., entitled Dockable Computer System Capable Of Electric And Electromagnetic Communication, U.S. Pat. No. 5,522,089 to Kikinis et al., entitled Personal Digital Assistant Module Adapted For Initiating Telephone Communications Through DTMF Dialing, U.S. Pat. No. 5,799,067 to Kikinis et al., entitled Smart Phone Integration With Computer Systems, and U.S. Pat. No. 5,799,068 to Kikinis et al., entitled Smart Phone Integration With Computer Systems.